Magnetic tunneling junctions (MTJs) include a thin oxide barrier, such as a MgO or Al2O3, separating a ferromagnetic free layer with its magnetization free to rotate and a fixed or pinned layer with its magnetization fixed in space, such as through exchange bias by an antiferromagnetic layer. In these devices, electric current sets the free layer magnetization orientation depending on the current polarity. The resistance through the MTJ depends on the orientation of the free layer relative to the fixed layer due to the tunneling magnetoresistance (TMR) effect.
In existing MTJ devices, such as spin transfer torque magnetic random access memory (STT-MRAM) devices, the direction of magnetization of the free layer and fixed layer are collinear and lie in the film plane of the magnetic layers. In these devices, the initial current-induced torque causing the reversal is very small, and is strongly dependent on magnetization fluctuations due to temperature. This results in large (˜5 ns or longer) switching times. This negatively affects both the device speed and its energy dissipation, since the longer switching time (during which current is flowing through the bit) translates into a larger energy dissipated per switching event.